As a general matter, certain metal alkoxides have been widely prepared in the past by a process which involves the use of metal halides, alcohols, and ammonia as reagents. The ammonia was employed to force complete substitution of halide and to scavenge the by-product hydrohalide, e.g. HCl, so as to remove it in the form of ammonium chloride. This removal of the HCl is important because of the side reaction between, for example, HCl and an alcohol taking place which would result in the formation of water and hence would undesirably hydrolyze the desired alkoxide product. In the case of forming a tertiary alkoxide the ammonia method is generally not satisfactory because the tertiary alcohols react quite rapidly with the HCl and the ammonia is not capable of removing the HCl effectively. The use of amines has also been described but not for tin.
Bradley, et al. (Chemical Society Journal, 1957, Part IV, page 4775 et seq. entitled, "The Preparation and Properties of Stannic Alkoxides") begin with the statement that "little is known about stannic alkoxides". In this article it is indicated, that in view of the successful preparation of alkoxides of titanium, germanium, zirconium, and hafnium through the tetrahalide, alcohol and ammonia method, they attempted to make pure stannic alkoxides from stannic chloride. It is indicated that the method did not yield pure stannic alkoxide. Success was obtained, however, in producing stannic tetra(tertiary-alkoxides) by an alcohol interchange process from tin ethoxide, the latter being prepared by the use of sodium ethoxide as a reactant. This technique, however, is a rather prolonged stepwise process and would not be economically justified.
In the Canadian Journal of Chemistry, Volume 39 (1961), page 1386 et seq., it is indicated by the present inventor that alkoxides may be prepared by reacting an alcohol with compounds having metal-nitrogen bonds, that is, compounds of the formula M(NR.sub.2).sub.x wherein M may, for example, be tin. The metal-nitrogen compounds are prepared by a reaction involving lithium diethylamide and those skilled in the art will readily appreciate the undesirable features of using such lithium compounds.
U.S. Pat. No. 2,269,498 indicates that amine compounds of Group IV metals can be produced by reacting a metal tetrahalide with an amine in an anhydrous solvent. While no tertiary alcohols are described as the solvent, in those instances where methanol is employed it may be that an alkoxide and an amine hydrochloride are formed, at least, as an intermediate product. This patent, however, has no recognition of a method for forming tin tetra(tertiary-alkoxides). Subject to this same deficiency in U.S. Pat. No. 2,901,452, wherein it is indicated that tin halide can be reacted with dimethylethanolamine and then treated with water and propylene or ethylene glycol.
U.S. Pat. No. 2,684,972 indicates difficulties in the art with regard to forming metal tertiary alkoxides, or metal esters of tertiary alcohols, and focuses on forming such metal tertiary alkoxides. While no examples are given it is prophetically indicated that tin tertiary alkoxides could be formed by the two-step process disclosed therein. In column 8 of this patent, it is indicated that the method of that patent eliminates the use of expensive organic amines such as pyridine. Presumably this statement contemplates the elimination of the combined use of pyridine and ammonia as set forth in the Nature article disclosed in column 1 thereof. The process of this patent, however, is not suitable for purposes of the present application, as will be seen by reference to the examples herein.
Chemical Abstracts, Volume 61 (33-Aliphatic Compounds) 1451E, entitled "Preparation of Stannic Ethoxide", discloses a process wherein stannic tetrachloride, ammonia, and ethyl alcohol is employed. There is no indication in that abstract of a technique for producing stannic tetra(tertiary-alkoxides) however.